Skip to Main Content


ACRIMSAT mission graphic

Active Cavity Radiometer Irradiance Monitor

Phase: Past

Launch Date: December 20, 1999

Program(s):Earth Systematic Missions

Pin it

The purpose of the Active Cavity Radiometer Irradiance Monitor III (ACRIM III) instrument is to study total solar irradiance from the Sun. The ACRIM III package is flying on a spacecraft called ACRIMSAT. The spacecraft was launched on December 20, 1999 as a secondary payload on a Taurus launch vehicle. ACRIM III, third in a series of long-term solar-monitoring tools built for NASA by the Jet Propulsion Laboratory, will continue to extend the database first created by ACRIM I, which was launched in 1980 on the Solar Maximum Mission (SMM) spacecraft. ACRIM II followed on the Upper Atmosphere Research Satellite (UARS) in 1991.

ACRIMSAT data will be correlated with possible global warming data, ice cap shrinkage data, and ozone layer depletion data. It is theorized that as much as 25 percent of the Earth's total global warming may be solar in origin due to small increases in the Sun's total energy output since the last century. By measuring incoming solar radiation and adding measurements of ocean and atmosphere currents and temperatures, as well as surface temperatures, climatologists will be able to improve their predictions of climate and global warming over the next century. Energy forecasting, carbon management, public health.

The science objectives of the ACRIMSAT Mission derive from the fields of climatology and solar physics. Small, sustained changes in the total solar irradiance of as little as 0.5% per century could be the primary causal factor for significant climate change on time scales of many decades. There is evidence that this has occurred in the past. Resolution of a century of TSI variation will require the flight of many instruments with overlapping missions to maintain the high precision of the data necessary to "see" the solar variability.

On the shortest time scales, solar global oscillations of low degree have been detected in the ACRIM I total irradiance data. This data may give us insights into pressure mode waves and gravity mode waves within the Sun.